TY - JOUR
T1 - Climate fluctuations and the spring invasion of the North Sea by Calanus finmarchicus
AU - Heath, Michael R.
AU - Backhaus, Jan O.
AU - Richardson, Katherine
AU - McKenzie, Eddie
AU - Slagstad, Dag
AU - Beare, Douglas
AU - Dunn, John
AU - Fraser, John G.
AU - Gallego, Alejandro
AU - Hainbucher, Dagmar
AU - Hay, Stephen
AU - Jonasdottir, Sigrun
AU - Madden, Heather
AU - Mardaljevic, John
AU - Schacht, Andreas
AU - European Union - MAS2-CT94-0085 (Funder)
PY - 1999/9
Y1 - 1999/9
N2 - The population of Calanus finmarchicus in the North Sea is replenished each spring by invasion from an overwintering stock located beyond the shelf edge. A combincation of field observations, statistical analysis of Continuous Plankton Recorder (CPR) data, and particle tracking model simulations, was used to investigate the processes involved in the cross-shelf invasion. The results showed that the main source of overwintering animals entering the North Sea in the spring is at depths of greater than 600m in the Faroe Shetland Channel, where concentrations of up to 620m -3 are found in association with the overflow of Norwegian Sea Deep Water (NSDW) across the Iceland Scotland Ridge. The input of this water mass to the Faroe Shetland Channel, and hence the supply of overwintering C. finmarchicus, has declined since the late 1960s due to changes in convective processes in the Greenland Sea. Beginning in February, animals start to emerge from the overwintering state and migrate to the surface waters, where their transport into the North Sea is mainly determined by the incidence of north-westerly winds that have declined since the 1960s. Together, these two factors explain a high proportion of the 30-year trends in spring abundance in the North Sea as measured by the CPR survey. Both the regional winds and the NSDW overflow are connected to the North Atlantic Oscillation Index (NAO), which is an atmospheric climate index, but with different time scales of response. Thus, interannual fluctuations in the NAO can cause immediate changes in the incidence of north-westerly winds without leading to corresponding changes in C. finmarchicus abundance in the North Sea, because the NSDW overflow responds over longer (decadal) time scales.
AB - The population of Calanus finmarchicus in the North Sea is replenished each spring by invasion from an overwintering stock located beyond the shelf edge. A combincation of field observations, statistical analysis of Continuous Plankton Recorder (CPR) data, and particle tracking model simulations, was used to investigate the processes involved in the cross-shelf invasion. The results showed that the main source of overwintering animals entering the North Sea in the spring is at depths of greater than 600m in the Faroe Shetland Channel, where concentrations of up to 620m -3 are found in association with the overflow of Norwegian Sea Deep Water (NSDW) across the Iceland Scotland Ridge. The input of this water mass to the Faroe Shetland Channel, and hence the supply of overwintering C. finmarchicus, has declined since the late 1960s due to changes in convective processes in the Greenland Sea. Beginning in February, animals start to emerge from the overwintering state and migrate to the surface waters, where their transport into the North Sea is mainly determined by the incidence of north-westerly winds that have declined since the 1960s. Together, these two factors explain a high proportion of the 30-year trends in spring abundance in the North Sea as measured by the CPR survey. Both the regional winds and the NSDW overflow are connected to the North Atlantic Oscillation Index (NAO), which is an atmospheric climate index, but with different time scales of response. Thus, interannual fluctuations in the NAO can cause immediate changes in the incidence of north-westerly winds without leading to corresponding changes in C. finmarchicus abundance in the North Sea, because the NSDW overflow responds over longer (decadal) time scales.
KW - calanus finmarchicus
KW - circulation
KW - modelling
KW - north atlantic
KW - aorth atlantic oscillation index
KW - norwegian sea
KW - deep water
KW - plankton
KW - winds
U2 - 10.1046/j.1365-2419.1999.00008.x
DO - 10.1046/j.1365-2419.1999.00008.x
M3 - Article
SN - 1054-6006
VL - 8
SP - 163
EP - 176
JO - Fisheries Oceanography
JF - Fisheries Oceanography
IS - s1
ER -